To reduce the chemicals used in the laundry washing process it has been proposed to decrease the builder salts in laundry detergent formulations. Without other formulation changes, this reduction could adversely affect the performance of the composition in hard water. It has been proposed to ameliorate this problem by using surfactant blends that are tolerant of the presence of hardness ions in the wash water, in particular blends tolerant to calcium ions. These surfactant blends have been termed “calcium tolerant surfactant blends”.
For the detergent formulator use of such calcium tolerant surfactant blends poses a new problem. Builder materials have often been included in the formulation not only to provide hard water detergency performance, but also to enable efficient manufacture of free flowing granular detergent formulations. Thus, reduction of builders in a formulation, whilst leaving it in the form of free flowing particles, is not straightforward.
Extrusion of detergent compositions is known.
WO 9932599A1 describes a method of manufacturing surfactant particles comprising an anionic surfactant, wherein the method may comprise drying an anionic surfactant and subsequently extruding through apertures, at an elevated temperature, the dried anionic surfactant, optionally blended with, builder, water, polymer and/or nonionic surfactant, and forming the extruded strands into particles, e.g. by cutting and spheronising. The apertures may comprise plain cylindrical apertures of diameter not exceeding 2 mm.
In WO 9932599A1 the material fed to the extruder is preferably an anionic surfactant paste, whose activity (i.e. anionic surfactant content) is most preferably at least 90% wt. The preferred materials of high activity may be prepared by subjecting the as-prepared surfactants to a drying step prior to the extrusion step. Examples of equipment which can achieve this include a rotary drum dryer, or a Chemithon Turbo Tube® drier, or, most preferably, a wiped film evaporator. Preferably, the dried product is a waxy or pasty solid at ambient temperature.
In one preferred method, a feed material comprises an anionic surfactant which contains 2-10% wt of water, and whose activity is 90-98% wt. It is found that the presence of this water aids the processing of the surfactant, within the extruder and/or during a downstream spheronisation step, if carried out. Alternatively, a dried surfactant may be employed in the feed material, and there may be a separate addition of water to aid processing.
WO 9932599A1 states that in some detergent formulations it is desired to have extremely low quantities of water present, or none at all. In such formulations, a non-ionic surfactant may aid the processing of the anionic surfactant within the extruder, and/or their downstream handling. Thus, in one preferred method an anionic surfactant and a non-ionic surfactant are present. The weight ratio of non-ionic surfactant to the anionic surfactant is suitably up to 1 part, preferably up to 0.5 parts, of non-ionic surfactant per part of anionic surfactant (with reference to their active contents). A non-ionic surfactant, when present, may suitably be added at any stage prior to the stage of mechanical working in the extruder; thus it may be added to the material comprising the anionic surfactant prior to the prior drying step (if carried out); prior to the feeding of the material comprising the anionic surfactant into the extruder; at the same time as the feeding of the material comprising the anionic surfactant into the extruder; or subsequent to the feeding of the material comprising the anionic surfactant into the extruder, through a separate feed point, during or, more preferably, prior to the mechanical working thereof.
One preferred class of anionic surfactants disclosed in WO 9932599A1 comprise the alkali metal (preferably sodium) alkyl sulphates (PAS). Another comprises alkali metal (preferably sodium) alkylaryl sulphonates (especially alkylbenzene sulphonates (LAS)).
It is preferred that the particles contain a builder. A builder in particulate form is suitably added to the material comprising the anionic surfactant during or, preferably, prior to the mechanical working thereof. Preferably, the builder, when present, is added to the material comprising the anionic surfactant within the extruder. A builder, when present, may suitably be present in an amount of from 0.1-10 parts per part of the anionic surfactant (active content), by weight. When the anionic surfactant is, or is predominantly, an alkali metal alkylaryl sulphonate, the builder may suitably be present in an amount of from 0.1-5 parts per part of the anionic surfactant (active content), by weight, preferably 0.1-1, most preferably 0.15-0.5 parts, by weight. The main ingredients of the extruded particles are preferably anionic surfactant and builder.
According to WO 9932599A1 following the extrusion process, it may be necessary to change the appearance and handling characteristics of the extrudate strands. This may be conveniently achieved by means of “chopping” the extrudate to the required length. A spheronising procedure may be carried out, if wished, on the chopped extrudate.
In all examples of WO 9932599A1 the particles were chopped into pieces in standard manner and then spheronised to give roughly spherical particles of approximately 1 mm diameter. Examples 1, 3, 4, 5 and 6 used alkyl sulphate anionic surfactant paste (PAS). As will be clear from examples 1 and 6, PAS is an unusual surfactant. It can be extruded without much drying or without any inorganic builder structurant present. This is due to the known fact that it has a hardness of about 2 MPa, which is relatively independent of the amount of water in the paste at below 10% moisture. Thus, it could be broken up in example 1 and it could be extruded satisfactorily, without need for any inorganic structuring in example 6. This contrasts markedly with the LAS surfactant used in example 2 of WO 9932599A1. The skilled person is well aware that LAS-rich pastes are sticky. Thus, it is conventional to add large amounts of solid structuring and liquid carrying materials, especially if further liquid-like material such as non ionic surfactant is also being added. Note that example 2 does not use any nonionic surfactant.
Example 2 declares a water content of 2-4% (based on “100-active” as on page 5 lines 25-27 of the application). At such high water levels LAS is too soft and sticky to extrude and cut. Thus, high levels of solid matter are normally added, like the 42% builder solids added to the extruder in Example 2. If nonionic had also been added, as in other examples of WO 9932599A1, using PAS, even higher levels of the solid builder addition would have been needed. The nonionic surfactant added to the extruder would not be molecularly blended with the LAS and would tend to be squeezed to the outside of the extruded strands, making them even stickier in the absence of solid builder carrier material to “soak them up”.
WO 9932599A1 envisages that nonionic surfactant could be added into the anionic surfactant before it enters the extruder, rather than in the extruder. But it does not perform this variant and the additional benefits of doing it for LAS rich, rather than PAS rich, compositions are not disclosed. The surfactants are not disclosed to be dried to a moisture content of less than 2%.
GB1303479 describes the formation of a water-soluble cleaning composition by extrusion of particles of length 0.5-10 mm. and cross-sectional area 0.04-0.8 mm2 each comprising (a) a higher (C9-18) alkyl aryl sulphonate, (b) a lower (C1-3) alkyl benzene sulphonate, (c) an inorganic salt and (d) water. In one embodiment (Example 1), the dry ingredients are ground together in a mill, mixed with wet ingredients in a ribbon amalgamator and milled into ribbons, which are carried by conveyer belt to a plodder. The plodder is equipped with a wire mesh of 0.5 mm. openings and a perforated plate having holes, which taper from 12 to 16 mm, with the larger diameter at the exit. The material is extruded through the plate, cooled by an air jet and then carried on a conveyer belt through a further air flow to a granulator fitted with an 8-mesh screen, which breaks the extruded strands into the required lengths. This document proposes the addition of sodium aryl sulphonate as a hydrotrope, to get fast dissolution. Thus, in the examples, there are comparatively low levels of surfactants in order to make space for the high levels of hydrotrope and builders. The drying process appears to happen post-extrusion. The particles have small cross-sectional area and are relatively long at 3 to 4 mm.
Surfactant blends comprising linear alkylbenzene sulphonate (LAS) and at least one co-surfactant have been shown to provide excellent detergency, even in the presence of hardness ions. However, these blends tend to be soft and lead to sticky compositions that cake upon storage.
This is recognised in U.S. Pat. No. 5,152,932(A), which discloses neutralisation of PAS/LAS blends using concentrated caustic in a loop reactor. The neutralized product preferably has less than or equal to about 12% by weight of water.
It is most preferred that essentially no detergency builders or additional organic materials are fed into the continuous neutralization system. Mixtures of PAS and LAS are preferred because of improved dispersibility of detergent particles formed from a paste made with the mixture. The final ratio of PAS to LAS should be between 75:25 and 96:4, preferably between 80:20 and 95:5. Thus the compositions disclosed should have less than 51% LAS. The keeping of LAS to a lesser amount is preferred because the neutralized material is then not unacceptably sticky, yet the particles formed from the cooled paste are dispersible in 15.5° C. water. Paste made from alkyl benzene sulfonic acid alone is said to be soft, sticky, and therefore difficult to form into non-sticky, discrete surfactant particles.
When 73% active caustic is used, the molten paste ordinarily has between about 9 and 11% by weight of water. This water level is too high to render LAS rich compositions non sticky.
The process further contemplates the blending of PEG or nonionic with the anionic pastes. There are no examples using nonionic.
This document says that detergent particles can be formed in various ways from the neutralized product exiting the continuous neutralization system. The molten paste can be atomized into droplets in a prilling (cooling) tower. To avoid prilling at all, the molten paste can be simultaneously cooled and extruded, and cut or ground into desirable particle sizes. A third choice is to allow the molten paste to cool on a chill roll, or any heat exchange unit until it reaches a doughy consistency, at which point other detergent ingredients can be kneaded in. The resulting dough can then be granulated by mechanical means.
A fourth and preferred choice is to cool the molten paste into flakes on a chill roll, then grind the flakes to the desired particle size. If additional drying is required, the cooled flakes can be dried in a rotary drum with hot air or in a fluid bed prior to grinding.
There are no examples using extrusion. This disclosure teaches against the use of LAS rich systems. Example IV used LAS. Even with addition of PEG, the 9 wt % water cooled product is said to be solid in nature but much stickier than the PAS examples. Similarly the PAS rich example V (with some LAS) is said to have improved dispersibility compared to PAS alone as active, but that as the level of LAS is increased, the softness and stickiness of the particle increases. At high LAS levels, it is said that the particles are less suitable for use as detergent particles because of their stickiness. According to the data in this application, the best compromise between low stickiness and good dispersibility is an alkyl sulfate/alkyl benzene sulfonate ratio of about 88/12 i.e. a significant excess of PAS over LAS and a LAS content of well below 51%.
One solution to this stickiness/caking problem for high LAS blends that does not involve using builder in the mix is to enclose the detergent in a rigid capsule as proposed in WO2006/002755. This solution is excellent for use in washing machines but it has drawbacks when the dose needs to be fine tuned for the amount of laundry or water used, as is often the case for hand washing of laundry.
Yet a further solution is to coat the sticky granules. Such a stickiness reducing coating is described in U.S. Pat. No. 7,022,660(B1), which relates to detergent particles having a coating or partial coating layer of a water-soluble material.
The particle core may comprise a detergent particle, agglomerate, flake etc. The coated particles have a number of improved properties among which is that the coated particles provide improved clumping and flowability profiles to detergent products containing the particles. The particle coating layer provides a coating, which is crisper and non-tacky. While effective at improving flowability in all detergent products, it is particularly effective at preventing clumping in products containing surfactants which are more difficult to dry to a non-tacky state including nonionic surfactants, linear alkyl benzene sulfonates (“LAS”), and ethoxylated alkyl sulfates or in detergent products containing high amounts of surfactant actives (i.e. greater than about 25 wt % surfactant active).
While such a coating modifies the properties of the finished detergent particle, it does not solve the problem of providing a non-sticky and easily cuttable output from the extruder. In a production plant, the material exiting the extruder must be hard enough to cut into repeatable sized particles that does not deform as the cutter passes through it, stick neither to the cutter nor to each other. They must also be hard and non-sticky enough to be used, or to be stored and handled in bulk until they are coated if a coating is to be applied. This might entail them being put into a big bag and even transported to another plant. Thus the solution of applying a coating is not sufficient to solve the problem of stickiness of LAS that is not structured with large, typically 30% or more, amounts of inorganic particles
Thus, the present inventors sought a solution to the problem of caking of particulate detergent compositions comprising high active surfactant blends with a major part of LAS, which did not need a special unit dose storage container for the detergent particles of the composition, or use structuring of the particles with a high (>10%) incorporation high inorganic solids loading in the particles.